Quality of life-associated factors among patients undergoing coronary artery bypass surgery as measured using the WHOQOL-BREF

Summary This was a study of the pre-operative factors that influence quality of life (QoL) in patients with coronary artery disease and the relationship between pre-operative QoL and early outcome after coronary artery bypass surgery (CABG). Using the WHOQOL-BREF questionnaire, 283 patients who underwent isolated coronary artery bypass surgery were interviewed and scores were obtained for the physical, psychological, social and environmental components. The study found that the independent physical component predictors for higher QoL included male gender and diabetes mellitus, while the independent psychological component predictors were male gender and high ejection fraction. Males, diabetics and patients with low education levels had higher social well-being than others. Among the postoperative complications, only respiratory failure was found to have a relationship with physical and psychological components. Women with coronary artery disease who were candidates for CABG had lower scores than the men in respect of all components of QoL. Furthermore, a lower pre-operative psychological score in patients undergoing CABG can influence postoperative complications, especially respiratory failure.

The World Health Organisation defines quality of life (QoL) as 'an individual's perception of their position in life in the context of the culture and value systems in which they live and in relation to their goals, expectations, standards and concerns'. 1 The subjective nature of quality of life means that it can be conceptualised differently by different individuals and groups of people, and is influenced by age, gender, health status and cultural factors, among others. 2 For the purposes of this study, QoL was defined as a sense of well-being, meaning, and value or self-worth. 1 It has been demonstrated that the risk factors for coronary artery disease (CAD) influence QoL, and a reduction in exposure to these risk factors would imply lengthening of life and improved health-related QoL in patients. Smoking, closely followed by high alcohol consumption and obesity are most responsible for the loss of QoL in both men and women. 3 Also, diabetes mellitus, hypertension and dyslipidaemia impact negatively on QoL in patients with cardiovascular disease. 4,5 Patient perception of quality of life is also influenced by therapy. 6 Treatment of CAD risk factors, such as antihypertension therapy, improves QoL. 7 Quality of life has also been acknowledged as an important tool in the evaluation of people for entry into drug rehabilitation programmes. 8,9 The evaluation of QoL before coronary interventions can predict postoperative complications and mortality, 10 while improvement in the components of QoL as well as an overall sense of well-being are related to the improvements in physical status that typically follow cardiac surgery. 11,12 There are, however, few studies that explore the effects of pre-operative risk factors for CAD on different components of QoL in CABG candidates. This study was undertaken to determine the influence of pre-operative QoL factors on patients with CAD and to assess the relationship between pre-operative QoL and early outcome after the operation. The findings are based on the WHOQOL-BREF questionnaire, which was completed by a sample of Iranian patients before CABG.

methods
On admission to the surgical ward of the Tehran Heart Centre, patients who were scheduled to undergo isolated CABG between May and September 2006 were invited to participate in the study by the data manager. With their informed consent, 283 patients completed the WHOQOL-BREF questionnaire 13,14 prior to the operation.
The WHOQOL-BREF defines QoL as participants' perceptions of their position in life in the context of the culture and value systems in which they live and in relation to their goals, expectations, standards and concerns. QoL refers to individual subjective evaluation, which is embedded in a cultural, social and environmental context. This definition of QoL focuses upon respondent perceptions of the effects of disease and health inter-department of anesthesiology, tehran heart Centre, tehran university of medical sciences, iran MAhDI  Summation and calculation of the mean score for each domain was done. According to the methodology, we transformed domain scores to a 0-to 100-point scale by using the WHOQOL transformation table. 13,14 According to the mean of these component scores, patients were divided into two groups in each component: mean score = 56 and higher for physical component, mean score = 58 and higher for psychological component, mean score = 59 and higher for social component and, mean score = 56 and higher for environmental component. A higher score on this questionnaire indicates a better quality of life. A study by Nejat et al. 15 demonstrated good to excellent reliability and acceptable validity of this questionnaire in various groups of subjects in Iran.
In addition, each patient's medical history and early complications after surgery were collected through interviews and by physical examinations. The data analysed included (1) preoperative variables, namely general characteristics: age, gender, body mass index (BMI) and education level (primary education defined as primary school or less, secondary education characterised as secondary school level, and tertiary education defined as university/college levels or equivalent); 16 (2) pre-operative risk factors, namely, current smoking history (patient regularly smokes a tobacco product/products one or more times per day or has smoked in the 30 days prior to admission), 17 alcohol abuse (the use of alcohol despite recurrent adverse consequences), 18 opium dependence (according to the DSM-IV criteria for substance dependence, daily regular using of substances), 19 hypercholesterolaemia (total cholesterol = 5.0 mmol/l, HDL cholesterol = 1.0 mmol/l in men, or 1.1 mmol/l in women, triglycerides = 2.0 mmol/l), 20 family history of CAD (first-degree relatives before the age of 55 in men and 65 years in women), 21 hypertension (systolic blood pressure = 140 mmHg and/or diastolic = 90 mmHg and/or on antihypertensive treatment), 22 diabetes mellitus (symptoms of diabetes plus at least one of the following: plasma glucose concentration = 200 mg/dl (11.1 mmol/l), fasting plasma glucose = 126 mg/dl (7.0 mmol/l), plasma glucose two hours postprandial = 200 mg/dl (11.1 mmol/l)), 23 cerebrovascular disease, and peripheral vascular disease; (3) pre-operative cardiac status, namely, previous myocardial infarction (an acute event with abnormal creatine phosphokinase and troponin levels), Euroscore, and functional class; (4) pre-operative homodynamic status, namely, the number of defective coronary vessels and left ventricular ejection fraction.
In addition, we considered two criteria of a complicated postoperative short-term outcome: (1) in-hospital postoperative complications (existence of at least one of these complications: postoperative arrhythmias, wound infection, stroke and respiratory failure); (2) in-hospital mortality rate (sometimes termed operative mortality), defined as death in hospital before discharge. 24 After having described the sample and its main characteristics, we explored the variations in QoL subsequent to CABG and the predictors of these variations. Results were reported as the mean ± standard deviation (SD) for quantitative variables and percentages for categorical variables. Groups were compared using the Student's t-test for continuous variables and the chi-squared test (or Fisher's exact test if required) or Mantel-Haenszel chi-squared test for trend for categorical variables. The predictors exhibiting a statistically significant relationship with the QoL components in the univariate analyses were taken for a multivariate logistic regression analysis to investigate their independence. Odds ratios (OR) and 95% confidence intervals (CI) for OR were calculated.
Model discrimination was measured using the c statistics, which is equal to the area under the ROC (receiver operating characteristic) curve. Model calibration was estimated using the Hosmer-Lemeshow (HL) goodness-of-fit statistics (higher p-values imply that the model fits the observed data better). The data analyser was anonymous, and data collection and processing were approved by the institutional review board of our heart centre. P-values of 0.05 or less were considered statistically significant. All statistical analyses were performed using SPSS version 13 (SPSS Inc, Chicago, IL, USA) and SAS version 9.1 for windows (SAS Institute Inc, Cary, NC, USA).

results
Demographic characteristics of patients and common postoperative complications are summarised in Table 1. The most common risk factors for CAD in the patients studied were hyperlipidaemia (68.0%), hypertension (49.1%) and diabetes mellitus (42.2%). The majority of patients had three defective coronary vessels and about half of them were NYHA functional class II. Also, among postoperative complications, the most prevalent complications were arrhythmias (35.4%) and respiratory failure (14.9%).
The relationships between QoL component scores and both pre-operative CAD risk factors and postoperative complications were evaluated with univariate analysis (Tables 2-5). All four physical (p < 0.0001), psychological (p < 0.0001), social (p = 0.023) and environmental (p = 0.003) component scores were higher in men than in women. The physical component score in diabetic patients was higher than in non-diabetics (p = 0.005). Also, patients with higher ejection fractions had higher psychological scores (p = 0.019).
Patients with higher body mass index (p = 0.066) tended to have a high psychological score. Patients with lower levels of education had a greater sense of well-being from their social relationships and reported higher levels of sociability (p = 0.010).
Multivariate logistic regression analysis showed that among the pre-operative characteristics of patients, male gender (p < 0.0001) and diabetes mellitus (p = 0.002) for the physical component and male gender (p = 0.0001) and high ejection fraction (p = 0.018) for the psychological component were independent predictors of higher QoL. Also, men (p = 0.032), diabetics (p = 0.037) and patients with low education levels (p = 0.025) had a higher sense of social well-being than other patients (Table 6). Among postoperative complications, a relationship was found only between respiratory failure and the physical (p = 0.011) and psychological (p = 0.023) components, while no relationships were found between other early complications and the four components of QoL.

discussion
Modern treatments such as CABG in patients with CAD focus not only on improving life expectancy, symptoms and functional status, but also on several aspects of QoL. An improvement AFRICA in QoL is considered to be important as a primary outcome and in the determination of therapeutic benefit. 25,26 While the WHOQOL-BREF is one of the main tools that can be used to evaluate QoL, in Iran, patients undergoing CABG are not evaluated on this questionnaire. Therefore, in the present study, we considered the role of the WHOQOL-BREF questionnaire in the evaluation of different QoL components before cardiac surgery and their relationships with pre-operative risk factors.
In this study, we found that the men's scores were significantly higher than the women's in all four components of QoL. According to Dias et al., 27 men had a better perception of QoL than women, while women more frequently had a below-median physical score. In their study, female gender was a main independent predictor of both physical and psychological components of QoL in patients with acute coronary syndrome. 27 In another study, it was indicated that women had more physical, social and psychological dysfunction, and poorer overall health than men. 28 Rankin et al. found that women had more in-hospital complications, cardiac dysfunction and mortality than men. 29 Other studies have reported that men had improved outcomes over women. 30,31 However, more recent studies have reported that long-term outcomes for men and women were similar. 32 It has also been demonstrated that a multi-component lifestyle-changing programme focusing on diet, exercise, stress management and social support can successfully improve several components of QoL in women who underwent coronary interventions. 28 In fact, it seems that the gender differences in QOL can be explained by the position of women in relation to men in the family. Here factors such as women's sense of inability to care for others when they are ill or the extent and nature of support and care available to them when they, as care givers, become ill may be at play. In our study, a high physical score was found in diabetic patients. In a study by Botija Yagüe et al., 33 diabetes impacted negatively on all dimensions of their quality of life and the diabetic patients were not positively affected by intensive therapy for cardiovascular risk factors. 33 Pischke 34 and Dias 27 reported that in diabetic patients, especially women, poorer physical functioning was observed when compared to non-diabetics. In Herlitz's study, physical and psychological scores were similar in diabetic and non-diabetic patients. 35 However, higher physical and psychological scores in diabetics versus non-diabetics are unusual findings and deserve more investigation. Besides, the assessment of the efficacy of the WHOQOL-BREF questionnaire is necessary in more studies on diabetic patients.
Chan et al. 36 suggested that level of education has no significant bearing on the quality of life of patients with coronary artery disease. By contrast, we found that patients with lower education levels had higher social component QoL scores. This difference may be accounted for, in part, by the impact of education (and class) on patient expectations. It seems that the patients with higher levels of education were less satisfied with themselves and their personal relationships as well as other domains of social functioning. 37 By contrast, the patients with lower levels of education were more satisfied with their lives and had a greater sense of well-being. These findings on the relationship between education, QoL and health outcomes would have to be tested further in population-based studies.
Another important finding of this study is that there was a strong relationship between both the physical and psychological QoL components and postoperative respiratory failure. Patients with respiratory failure had lower pre-operative psychological scores. There are many studies on the effect of respiratory failure on QoL. However, we found no study on the effects of low scores of QoL on respiratory function. In a study by Euteneuer et al, it was indicated that in patients with chronic respiratory failure after long-term mechanical ventilation, physical health was markedly reduced compared to the general population norm, but mental health was only mildly impaired. 38 Patients with respiratory failure are seriously handicapped mentally and physically compared with those with other diseases. This is because their disorders relate to breathing, which is the basic physical function directly associated with sustaining life. 39 In general, we found that women with coronary disease who became candidates for CABG had lower scores than men in all QoL components. Education levels influenced patient QoL albeit not in an obvious way. Also, diabetic patients may have had better physical functioning than non-diabetics. This latter finding requires further investigation, as it is unexpected. Lastly, lower pre-operative psychological scores in patients undergoing CABG can influence postoperative complications, especially respiratory failure.